It is very old to provide means for testing the brakes of an automotive vehicle by providing tread plates, one for each wheel of the automotive vehicle and resiliently restraining these tread plates against longitudinal movement so that any movement that does take place is dependent upon the braking force existing as a result of the application of the brakes while the vehicle is moving over the tread plates. This movement of the tread plates is used to indicate the effectiveness of the brakes for each wheel. This may be done by the use of some form of transducer which supplies a signal to some indicating device on a central pedestal. Often, this transducer takes the form of a hydraulic control. On the other hand, it is also old to use an electrical transducer. Normally, the individual transducers are employed to indicate the braking force at each wheel. It is also old to sum the effects of the various transducers to produce an indication of the total braking force that is available.
In order to evaluate the adequancy of the total braking force available, it is necessary to compare this with the weight of the vehicle. Obviously, the heavier the vehicle and its load, the greater is the braking force that is needed to stop the vehicle properly. Unfortunately, it has been very difficult in the past to accurately determine the weight of the vehcile unless the vehicle is first driven on to scales designed for that purpose. This is not suitable where the testing must be done in a relatively small area. Furthermore, it involves two different steps and the correlation of the weight as determined by the weighing mechanism with the braking force as determined by the brake tester. In addition, where the transducer is a hydraulic one, this involves the use of hydraulic lines between the transducer which must normally be close to the tread plate and the indicating pedestal. There is also some delay introduced by reason of the action of the hydraulic system. Even where an electrical transducer has been used, the system employed is normally one using analog signals and the amount of arithmetical functions which may readily be performed are limited.